1. Field of the Invention
The present invention relates to discharge of impurities in a fuel cell system for generating electricity by means of an electrochemical reaction between hydrogen and oxygen.
2. Description of the Related Art
In recent years attention has been focused on fuel cells that generate electricity by means of an electrochemical reaction between hydrogen and oxygen as an energy source. In this type of fuel cell system, when the ambient temperature goes down to sub-zero while the system stops operating for a while, water inside the fuel cell system may freeze, resulting in a impediment to operation. Further, there is also the possibility that this freezing might degrade the fuel cell system. There has been proposed a water trap for temporarily accumulating water and then discharging the accumulated water from a discharge port of the water trap to the outside (for example, JP2002-313403A).
It is preferable to discharge water accumulated in the water trap in a manner such that the water does not freeze when temperatures are low. The accumulated water can be detected by means of a water level sensor in the water trap. There is a chance, however, that the range a water level sensor can detect water will be limited. For example, when the quantity of accumulated water is small, there is a chance that water level sensor may not be able to detect the water. In this case, there is a possibility that water may not be detected and remain in the water trap.
In another method, the accumulated water may be discharged by opening the discharge port for a fixed time. The quantity of water accumulated in the water trap, however, depends on the operating conditions of the fuel cell. As a result, when there is a large quantity of accumulated water, the opening time of the discharge port will be insufficient, resulting in substantial quantity of water being left in the water trap.